Digital cameras capture and store a large number of digital images. Fortunately, the capacity of memory cards used to store these images is increasing so that the cards are able to hold larger and larger numbers of images. Working against this increasing capacity in memory cards is the increasing resolution of image sensors in the cameras, which require the creation of larger files to store each individual image. The total number of images that can be stored on a particular memory card is proportional to the size of the memory card, the resolution of the images, and the effectiveness of the compression algorithms used to reduce the storage needed for each image. Some images are not compressed, while others are compressed with algorithms such as used in the JPEG standard, yielding smaller image files. Certain features of some more advanced digital cameras make it easy to fill up a memory card with large numbers of images. Two features, in particular, create a rapid succession of images in a short period of time. One of the features is bracketing, where a succession of several images is captured, each with a slight variation of certain camera settings. The other of the features is a repetition mode, in which the user can take a sequence of images, possibly by holding the shutter down. The former feature is useful when it is hard to set the camera for a certain exposure. The latter feature is useful for taking pictures of an object that is changing, such as a child that may not be smiling when the first picture is taken, but may subsequently smile when the second, third or fourth pictures are taken. There are other features that may also produce a series of similar images. In both instances, there is a high probability that certain aspects of each captured image will be similar or the same. For example, the backgrounds may all be similar while the subject may change in each frame.
Having these features may also create another problem, in that, taking so many images may quickly fill the user's memory card with sets of similar images. Still image compression, such as JPEG, may reduce the overall size of each individual image, but, at perhaps a megabyte per image, taking several sets of 4 to 5 images in rapid succession may quickly fill up even the highest capacity memory card. Another problem is the number of images that fit within the camera's higher-speed temporary memory. When taking the succession of images, current technology stores each image of the succession in a higher-speed temporary memory before moving to longer term storage, perhaps because there isn't sufficient time to store each image on a memory card. Since the higher-speed temporary memory is limited in size, only a small number of successive images may be stored within such memory. If a better compression method was available, a greater number of successive images could be captured.
Therefore, it would be desirable for a multi-image compression mechanism that will recognize a series of images and use motion encoding compression schemes to further compress the series of images.